Grinding mill and process of operating it



July 10, 1934. R. M. HARDGROVE GRINDING MILL AND PROCESS OF OPERATING IT2 Sheets-Sheet '1 Original Filed Feb. 12, 1930 may NVENTOR TORNEY6 July10, 1934. R. M. HARDGROVE 1,955,643

GRINDING MILL AND PROCESS OF OPERATING IT Filed Feb. 12. 19302,Sheets-Sheet 2 I VENTOR [2 iv M /MW Patented July "'10, 1934 UNITEDSTATES PATENT OFFICE GRINDING MILL AND PROCESS OF OPERATING IT Ralph M.Hardgrove, Bethlehem, Pa... assignor to Fuller Lehigh Company,Fullerton, Pa., a corporation of Delaware 11 Claims. (01. 83-44) Thisinvention relates to a grinding mill of the type in which solid materialis finely ground or pulverized and the finely ground particles areremoved from the mill by a current of air. The

invention is especially useful in connection with grinding coal but isnot restricted to this particular use.

Heretofore difiiculties have been experienced in regulating the feed ofmaterial to a mill of this sort so as to have a proper amount of thematerial in the mill as it is undergoing the grinding operation. By thepresent invention the rate at which the material is introduced into themill is automatically regulated to keep the proper l5 amount of thematerial in the mill.

The invention will be understood from the description in connection withthe accompanying drawings, in which Fig. 1 is a side view, partly invertical section, showing an illustrated embodiment of the invention;and Fig. 2 is a similar view showing a modification.

In the drawings reference character 1 indicates a grinding mill with aseries of grinding balls 2 in the lower portion thereof, these ballsbeing driven in a well-known way by means of a motor 3.

An inlet 4 for air extends into one side of a casing 5 of the mill, sothat air passes from the inlet 4 into the annular space between theinside wall of the casing 5 and the outside wall of the annular baille6. Air may be forced to pass through the mill from the inlet 4, asindicated by arrows, to pick up fine particles of the material that isbeing ground by a blower, not shown. Or the air may be drawn through themill by means of a suction fan, not shown. Arrangements for causing acurrent of air to pass through such mills are old and well known and itis not thought necessary to describe them in detail.

Material such as lumps of coal, for example,

is fed into the mill by means of a feeder 7. The rate of feed ofmaterial into the mill depends upon the speed of the feeder motor 7. Thematerial enters the mill through an opening 8 and since feeders of "thistype are well known in this art, it is not thought necessary to describeone of them in detail. I

The upper portion of the mill 1 is provided with a separating cone 9with an open bottom 10. The dust-laden air passes over the upper edge 5of the cone 9 and out through the outlet 11, the large particles passingback through the outlet 10 for further grinding. The mechanism forregulating the rate of feed of material to the mill in accordance withthe amount of the material in the mill, will now be described. Arestricted orifice 4' is provided in the inlet 4 to cause an appreciabledrop in pressure of the air as it passes through this orifice. Pipes 12and 13 lead from opposite sides of the orifice 4' to a wellknown type ofpressure differential device. This device comprises an invertedstationary hood or bell 14, the lower edge of which extends below thelevel of liquid in a container. The extension 12' of the pipe 12 extendsinto'the hood 14. A floating hood or cup 14' of small size is placedinside of the hood 14 and the extension 13' of the pipe 13 extends intothis hood. The hood 14' is connected by a rigid framework 15 andflexible connection 15 to one end of a lever 16 which is pivoted at 1'7and carries a mercoid switch 18.

The other end of the lever 16 is connected to a similar floating hood orbell. The hood or bell connected to this end of the lever 16 is operatedby a drop in air pressure in the mill 1 between the inner side of theorifice 4' and a point beyond the lower edge of the annual baflle 6. Apipe-19 extends from such a point in the mill 1 into a floating hood orbell 20 that is located in a larger stationary hood 20', into which abranch 13" of the pipe 13 extends. The floating hood 20 is connected bya rigid framework 21 and flexible connection 21' to the lefthand end ofthe lever 16.

Reference character 22 indicates diagrammatically a device of awell-known type which variesv the speed of the motors 3 and '7' inaccordance with the demand for the ground material. It is connected tothe motor 3 by means of a connection 23 and regulates the speed of thismotor. It is also connected to the motor 7' through a resistance 24which it varies in accordance with the speed desired. A resistance 25 isconnected in series with the field 26 of the motor 7' and wires 27 areconnected from the mercoid switch 18 to one side of the resistance 25and the resistance arm that passes over this resistance, respectively,and serve to short-circuit this resistance when the mercoid switch 18 isclosed. The resistance 25 is preferably set so that the speed of thefeeder motor 7' will be slightly greater than is necessary to feed theproper amountof material 100 into the mill 1 under normal conditions,sothat when the resistance 25 is cut out by the closure of the mercoidswitch 18 the speed of the feed motor will be decreased.

The pressure differential mechanism can be 105 adjusted so that thelever 16 will be in the horizontal position when the level of thematerial being ground in the mill 1 is at the desired point. The drop inpressure across the orifice 4' and the drop in pressure of theair p nhrough the 110 orifice between the lower edge of the bafile 6 and theupper surface of the material that is being ground, balance each otherunder this condition. When too much material accumulates in the mill 1the resistance to the passage of air below the baffle 6 is increased sothat an increased drop in pressure takes place through this orifice withthe result that the righthand end of the lever 16 rises and the mercoidswitch 18 is closed, this short-circuits the resistance 25 in the field26 of the motor 7', thereby decreasing the speedof the feeder mechanism,thus decreasing the rate at which the material is fed to the mill 1,without decreasing the speed of the motor 3 that drives the grindingballs 2.

An increase in the amount of air passing through the mill also increasesthe drop in pressure between the pipes 13 and 19. In order to preventthe change in the amount of air passing through the mill from changingthe speed of the feeding mechanism, the orifice 4' is provided so thatthe corresponding change will take place in the drop of pressure throughthis orifice 4, thereby compensating for corresponding changes in thedifferential pressure mechanism.

In the modification shown in Figs 2, instead of using a fixed orifice inthe air inlet, pipes 30 and 31 are connected to points on opposite sidesof the separator 9 so that the drop in pressure between these pipes willdepend upon the amount. of air passing through the machine. The drop inpressure of the air passing under the baffle, 6 or through the orificebetween the lower edge of this bafile and the upper surface ofthematerial that is being ground, can be, indicated bythedifference inpressure between the pipes 30 and 32. The pipes 30, 31 and 32 areconnected to p. pressure differential mechanism similar to that de-'scribed in connection with Fig. l and it is not believed'that it isnecessary to repeat the description. In this modification the pipes 30and 31 are connected to one side of a visual pressure indicatingmechanism 33 and the pipes 30 and 32 are connected to the other sidethereof. This mechanism 33 is provided with lines 34 along the ends ofwhich pointers 35 and 36 actuated by the differentials in pressurebetween the pipes 30 and 31 and pipes 30 and 32, move. This device isalso old and well known and it is not believed that it is necessary todescribe the same.

I claim: a

1. The process of controlling the feed of material to an air-sweptgrinding mill, which comprises passing air through the mill andutilizing variations in drop in the air pressure through an openingthrough which the air passes in the mill, that varies in size inaccordance with the amount of material in the mill, to vary the rate offeed of material to the mill.

2. Theprocess of controlling the feed of material toan air-sweptgrinding mill, which comprises passing air through the mill andutilizing variations in drop in the air pressure through an openingthrough which the air passes in the mill, that varies in size inaccordance with the amount of material in the mill, to vary the rate offeed of material to the mill, and regulating said control by the drop inpressure of the air as it passes through an opening of constant size.

3. The process of controlling the feed of material to an air-sweptgrinding mill, which comprises passing air through the mill to removefine particles of ground material, causing the air to pass through anopening of constant size and an opening whose size varies with theamount of material in the mill, and utilizing the drops in pressuresthrough said openings to vary the rate of feeding material to the mill.

4. The process of controlling the feed of material to an air-sweptgrinding mill, which comprises passing air through the mill and creatinga drop in pressure at one place, creating a drop in pressure at anotherplace in accordance with the amount of material in said mill that isbeing ground, and utilizing the difference in saiddrops in pressure tocontrol the rate of feed of material to said mill.

5. The process which comprises passing air through a grinding mill topick up fine particles of ground material and controlling the rate offeed of material to the mill by a drop in pressure which depends uponthe amount of air entering the mill and another drop in pressure whichdepends upon the amount of material in the mill.

6. The process which comprises introducing coal into a grinding mill,passing a current of air across the surface of the'coal in the mill andcontrolling the rate of introducing the coal by the resistance to thepassage of the air over the surface of the coal.

7. The process which comprises introducing coal into a grinding mill,passing a current of air across the surface of the coalin the mill andvarying the rate of introducing the coal by variations in the resistanceto the passage of the air over the'surface of the coal in accordancewith the ievelgof coal in the mill.

8. In combination, a grinding mill, means for feeding material to saidmill to be ground, means for passing a current of air through said millto pick up fine particles of material, means for creating a drop inpressure at one point, means forv creating a drop in pressure at anotherpoint in said mill in accordance with the amount of material in saidmill that is being ground, and means (or controlling said feeding meansby difference in said drops in pressure.

9. In combination, a grinding mill, means for feeding material to saidmill to be ground, means for passing a current of air through said millto pick up fine particles of material, means providing a fixed orificethrough which the air passes, means providing an orifice, that varies insize with variations in the amount of material being ground in saidmill, through which the air passes and means operated by pressure dropsthrough said orifices for regulating said feeding means.

10. In combination, a grinding mill, means for feeding material to saidmill to be ground, means for passing a current of air through said millto pick up fine particles of material, means providing two orificesthrough which the air passes, one of said orifices being of fixed sizeand the other varying in size in accordance with the amount. of materialin said mill, and means operated by pressure drops through said orificesfor regulating said feeding means.

11. In combination, a grinding mill, means for feeding material to saidmill to be ground, means for passing a current of air through said millto pick up fine particles of material, means providing two orificesthrough which the air passes, one of said orifices being of fixed sizeand the other varying in size in accordance with the amount of materialin said mill, and means connected to opposite sides of said orifices toregulate the rate 01 feed or material to said mill.

RALPH M. HARDGROVE.

